Document MJmpzvYad51oYw4vr26mG1J6y

'Ab J t. ' / /\ '/ A- / 7'^ Archives of R&S 024239 ^x-:`r'*a' '' :":-:^r: Volume 48>i.VNumber 4 ,* November 1981 Last issue of this volume ."SWL v4s?; Origins/ //)vestigations H. M. Bolt, J. G.FBser, A. Boehter: Inhalation Pharmacokinetics Based on Gas Uptake Studies. - /A Pharmacokinetics Assessment in Man of "Peak Concentrations" of Vinyl Chloride ii&SASi'ri' , i ` . ..('i ' V?',' '' 'fiS&tji'-rra ' a' 'tuw,hi,>uJn*>M''An Annrrvnrh Towards the'Standardizatlon of the Mammalian Spot Test 253 '/ 265 ` ' B. D. GotdstebvH^' E/Lowndes, E.-S. Cho: Neurotoxicology of Vincristine In the Cat Bectro- physiological Studies. '-- Vr- ... . M. loni, S.D.rFerrara, S. CarokJl, F, Sinlgsglia: Enzyme Studies with Human and Hen Autopsy Tissue Suggest Omethoate Does not Cause Delayed Neuropathy in Man 271 S. G. Schafer. G. N*; C. H. Henning; Movement of Thallium (I) Iona in vitro 281 C. Steffen, R. Seitz; Severe Chlorate Poisoning: Report of a Case ': Short Communication w. Drtmfrt*Jd.:'a frejanowska; Chromatographic Determination of Thiodigtycolic Acid - a Metabolite of Vinyl Chloride . '%jjjn}/233, ' .. C.-P. Sieger*. R. pentz. J. Degef&nde: VerstSrfct Alkohol die Toxizitit von Papequat? , Does Alcohol Enhance the Toxicity ofParaquat? ' r- Indexed in Current Contents , - " ' 'Cr'f.O' 'i-y Meeting Announcement The 8th European Workshop on Drug Metabolism win be held at tha University of Liege. Belgium, September 5-9,1382. For further information, please contact: Professor Jacques . Gielen, Laboratoire de Chimie MAdicale, Institut de Psthologie, UniversitA do LiAge, BAtiment B 23, B-4000 Sari Tilman par LiAgo 1, Belgium, telephone (32-41 >-56.24.80/81. 'rj?.i A .....W- l-'.-.A ....IL'. ... , .. - * .... .. ` . . 1 . , 1 tflt ADTAriN a S (ICl 1 \ srw** *v**.' c) ft:/ \i.ii i. m,.-I i ; TOXICOLOGY ()ri"inal hi i 'estimations Inluilation Pharmacokinetics Based on (>as Uptake Studies III. A Pharmaeokinclie Assessment in Mini <f "Punk Concentrations" of Vinyl Chloride II. M. Hull1. .1. (i. 1-iKcr. .mil A. Buchiei ' ' Ahlciluni: lur loMkolikMv l,h.irnuik`Ut:fA.'lK,s In-stitut dor I'iihi.'imI.ii M.mi/ Ohoro AihlKkher NimIW fC IMAki M.un/ i itlslilul uiul I'n'iklmik tui Ailk'i's uihJ S vulniviii/in dot l hiummUii K"!n li>soI-Slol/m.inn-Mr. ,,M. ! miMM k.<ln 11. I otJoi.il KipuNk o\ <icrm.Mi\ Abstract. On the basis of previous determinations ut pharmacokinetic parameters lor inhaled vinyl chloride tn men, rhesus monkeys. and rats, and on improved pharmaeokinetie models a pharmacokinetic tieatment ot the problem of "peak concentrations" of vim! chloride, as occurmg m industrial practice, became possible. l or the calculations, metabolic elimination kinetics of vinyl chloride was assumed 10 be lirst order as experiments in diflerenl species including rhesus monkeys showed "linear" phaimacokineties up to atmospheric exposures of 200 - .''till ppm. I he distribution o! vinvl chloride between atmosphere and organism under ihtlerem conditions was evaluated using "sieadv-xiate-kinetics". After treating the processes ot "influx", "elflux". and "metabolism", the numerical mines t.u the parameters denied from a human kinetic experiment wvic used lo theoretically calculate the time courses ot coneeiilration ot smyl chloride in the orcanism and ot the cumulative amount ot vinyl chloiide metaboli/ed, under the conditions ot (a) a 2 h constant exposure to ppm vinyl chliuide and (b) two subsequent "peaks" of 50 ppm with a duration of 5 mm each This model calculation suggested that, regardless ol the exposure protile, the amount of (reactive) metabolites formed from vinyl chloride would soleley be a function of the mean atmospheric vinyl chloride concentration oiei tune. The general mliditv of this suggested rule could subsequently be demonstrated. As the coneeiilration of the reactive metabolite ol vinyl chloride responsible loi the eaicinogcmc elfect at the target site must be a icsultani of both tormation and inactii ation. an evaluation ol the ditleretitial tisk of different exposute profiles can reasonably be based on biochemical examinations ol the "detoxifying" pathways. This points out the relevance ol studies of the patterns ut hi Here at metaboliies ot vinyl chloride m man uiulei vanuig exposure profiles Key words: Vinyl chloride - Pharmacokinetics - Peak concentration Inhalation kinetics o.s4il SI tHij.s 11215 s iA 2b R&S 024240 :> i 11 \l It..it , ! ,i Introduction Considerable ellorts have been directed towards developing a genera! concept lor the limitation of "peak concentrations" ol hazardous chemicals at the workplace. Proposals have been elaborated lor non-carcmoeemc conmpoumls (llenschler 1979) which tire based on both pharmacokinetic pounds and classical dose-response considerations. l;or carcinogens. a sound sctentitic basis for such an assessment is lacking so far. To promote a further discussion ol this mailer, the present paper describes one part of the situation, from a pharmacokinetic viewpoint, dealing with an outstanding example. unyl chloride. There is now sufficient evidence that the carcinogenic principle ot vine I chloride is a reactive metabolite, most probably chlorocthylene oxide, another reactive metabolite is the product of spontaneous rearrangement of this epoxide, chloroacetnldelmle (Guengerich et al. BP9; Zajdela el al. 19S(J; Boh ei al, 1980). Because the initial step of metabolism of vinyl chloride is epo.xidation by (microsomal) monoo.xygenases, this means that the overall metabolic elimina tion of vinyl chloride which can be determined in vivo bv phaimacokincnc methods, must be equivalent to the total amount of epoxide produced. Interesting proposals have been published (Gehring et al. 1978. 1979. Anderson et al. 1980) to incorporate pharmacokinetic data of vinyl chloride into calculations of dose-responses and into risk assessment. Such models imply, either explicitly or tacitly, that the response (cancer development) is a function of reactive metabolites produced over time, rather nan a function of plein atmospheric vinyl chloride exposure. Hence, calculations of the actual amounts of vinyl chloride metaholi/ed by the human organism under various conditions of exposure, upon careful observation of the implicit limitations, could give some idea of the risk of these exposures, and could possibly contribute to tackle the outstanding problems mentioned above. Such calculations can now be based on expanded models lor inhalation pharmacokinetics (I-ilscr and Bolt 19S1) and on appropriate experimental data for vinyl chloride in rats (l-'ilser ami Bolt 1979). rhesus monkeys (Bucliter et al. 1980). and in man (Buchter ei al. 1978; Buchter 1979). In the United States, a threshold limit value ("TLV") of 5 ppm has recently been adopted for vinyl chloride (ACG1II 1980). In the T'ederal Republic of Germany, a "TRK" value of 2 ppm (or 5 ppm for pre-existing plants) is in force (see Df-`G 1980). Other countries have similar regulations. However, it is well documented that in industrial practice multiple peak concentrations do occur w hich by far exceed 5 ppm vinyl chloride (Baker and Reiter 1977). Most of these peaks (which may occur several times a day) have a duration of a few- minutes only; individual peaks may even reach concentrations of 50 ppm and more. Because the influx of vinyl chloride into the organism is a time-dependent process, it was suggested (Buchter et al. 197S) that very short single peaks did not considerably contribute to the overall load of vinyl chloride metabolites in the organism when compared to a constant exposure to the allowable "TI.V" or "TRK". However, a quantitative treatment was not possible at that time bceau-e of the lack of appropriate pharmacokinetic tools. X mil < hint.tii I't.ilt ( i 1 he present pa pet desc elimination ol vinyl ddorn has been mentioned abovi produced I Ills now provi, [liolilem ot varying expos Pharmacokinetic Model l ust of all. the non-lmca observed w hile selecting a chloride follows lirsi-ordei 25b ppm (l-'ilser and Boll become saturated. The the discussed in detail (l-ilxei displaying a quantitative n man. the same saturation (Buchter et al. lVS-Jl. and m up to u'mosphcric vinyl chic carcinogenicity of vinyl chl< verify this saturation patter data obtained from rats at suggests that also in man lin fact observed tit very low e> be valid up to atmospheric entirely the range within w practice, we decided to pharmacokinetic modd. bca lor exposures up to 2<X)3` Pharmacokinetic Data in 5 `The basic pharmacokinetic c published (Buchter et al. 197 this material. At low vinyl "dosed" and in tin "open" sy ,ur were monitored) gave sir .mee of vinyl chloride from th miermdividual variation in t winch, according to animal c: i differing mass of adipose tinumeric calculations of this determined in one individun 1979). By analogy to the denom conditions of the experiment ;-*sh R&S 024242 hv , esc j SUs I'/'; V im) Cliliirnk' IV-ik ( minim.linin'. :i' The present p;iper describes. under various conditions, tlie i ates ot metabolic eluuination of vin> I chloride from the human organism which. according to v.h.ii has ncen menlioned above, is equivalent to the rates ol epoxide mciabohcalB produced. Tills now provides pari ol the basis loi a scientilic vs.dilation ot the problem of varying exposure profiles ol vinyl chloride. Pharmacokinetic Model First of all. the non-linearity of pharmacokinetics of vinyl chloride must be observed while selecting a kinetic model. In rats, metabolic elimination ot vinyl chloride follows first-order kinetics if atmospheric exposure does not exceed 250 ppm (Filscr and Holt 1979), Above this point the metabolizing capacities become saturated The theoretical implications of this phenomenon have been discussed in detail (Filscr and Bolt HIM). In rhesus monkeys, a species displaying a quantitative metabolic pattern of vinyl chloride much similar to man. the same saturation point of vinyl chloride metabolism was observed (Buchteret til. 1980), and metabolic elimination again followed a first-order rule up to atmospheric vinyl chloride concentrations of 2(H)-3(K) ppm. Because ol the carcinogenicity of vinyl chloride human experimentation in this dose range, to verify this saturation pattern, is not possible. However, the close agreement of data obtained from rats and from a primate species in this particular point suggests that also in man linear pharmacokinetics of vinyl chloride which are in fact observed at very low exposure concentrations (Buchter et al. 1978) should be valid up to atmospheric concentrations of 200-200 ppm. Because this is entirely the range within which "peak concentrations" do occur in industrial practice, we decided to exclusively base our calculations on a linear pharmacokinetic model, hearing in mind the implicit limitation that this is valid for exposures up to 200-300 ppm only. Pharmacokinetic Data in .Man The basic pharmacokinetic data on vinyl chloride in man have been previouslypublished (Buchter e: al. 1978; Buchter 1979); the present analyses are based on this material. At low vinyl chloride concentrations, experiments both ir. a "closed" and in an "open" system (where concentrations in inhaled and exhaled air. were monitored) gave similar metabolic clearance values for the disappear ance ot vinVl chloride In an fhe air. THtese'data a'lso -deinonsi' axed a interindividual variation in the distribution behaviour of \inyl chloride in man which, according to animal experiments (Buchter et al. 1977) ought to be due to a ditfering mass of adipose Tissue. Therefore, we decided to base all the specific numeric calculations of this report on the actual pharmacokinetic parameters determined in one individual only (subject "B": Buchter et al. 1978; Buchter I97U). By analogy to the denominations of Filser and Bolt (1981). the model and conditions of the experiment in question (Buchter et al. 1978: Buchter 1979) are `.v < summarized in Fig, la. In the dosed atmosphere of X I luilurac ol spirometer, containing air/vinvl chloride plus the residual breath volume) the actual decline of vinyl chloride given in Fig. 2a was measured. This decline followed the general function The numeric:)! *s whereby "vis obtained by extrapolation ol the second decline phase to C Cp? V,* ^^ V;* 81 'll 831 metabolism Kip. la iind b. Block ol pharmacokinetic systems (or inhalation Cp, ol vmyl chloride (numerical values ti b) influx ------ V efflux 831 k" > metabolism subject B.. Buchter ct al. J97S): (at inhalation from a closed cas phase as described in Buchier el tl IV7S and titi.hlcr (t>) translation of V, oo ^12 0 pharmacokinetic parameters into an "open** system ol exposure VC in 3r CQkulaicd uata** (>ji vC $os) Hj>. 2* and In Determination t>i pharmacokinetic parameters lor vmyl chloride in man: (a) experimental data obtained with subject B (Buehier ei al 147K; Buchter l*/?4*) in the air pha^e (Cpi) ol svsiem shots n in Fit., la. and extrapolation of the final logarithmic decline to r = d [y[ol||: (b) demonstration of the initial process of "equilibration", values being calculated from the experimental data of the first section ot the curve in panel (a) minus the coi responding points on the curve extrajHilated from the second phase, expressed as calculated gas uptake ot vinyl chloride (VC) J3 B (0 o Is) Is) 0) .''icu V| We obtained K = 1.35 constant" (Filscr and .. A`-> - i/ " .. ' , "*i 1 ? } it which is derived unc negligible metabolism."; concurrent metabolic cr ihe "steady state cons': Therefore. K (Eq. 2) e /CM (noi for Krq). From Holt. 1VSI). ke, (Fig. 1 mxi): a.., f he numerical value ft d ig, hi) we still do not the experimental curve cuustaiiis of the partial Ail exact volution of thi id this paper as Eq. ( A. R&S 024244 Vinyl Chloride Peak ('oiivirntraliuiis The numerical values of the rate constants were: i) = 29.7 h ' : A' = 1 .Vi) h 1 . These values were obtained by using a log regression ealeulaior program. I he highest coefficient of correlation (r = 0.9913) lor the second decline process was obtained when the experimental points after t = 20 nun were taken tor that calculation. These results differ slightly from those of a preliminary, merely graphical. evaluation of the decline curve (Buchter et al. 197S: Buchter 1979). From the values of .v1(li,. vj,,,,. the volumes of the air phase (l'|) and the organism (V:) the distribution of vinyl chloride was calculated which actually prevailed under the conditions of the experiment (Buchter 1979): K _ O'iwi " .viiui) ^i .Wmi Jt'ioi) ^sj We obtained K = 1.35. This K derived here is not identical with the "equilibrium constant" (Filser and Bolt 1979) k, l' V which is derived under theoretical conditions of a static equilibrium will; negligible metabolism. The conditions of distribution between Cp; and Cpi with concurrent metabolic elimination may appropriately be described by introducing the "steady state constant". A'M, as derived by Filser and Bolt (1981: Eq. 14). Therefore, K (Eq. 2) can be regarded as an experimentally obtained value tor k\, (not for A'Cl|). From A'sl and the metabolic clearance C7,,,, (Eq. 22 of Filser and Bolt. 1981), A0| (Fig. 1) can be calculated by using Eq. (26) of Filser and Bolt (1981): f A,-i - r~k\, (4) I'he numerical value for subject B is: kcl = 2,03 h-1. Ot the kinetic constants (Fig. la) we still do not know A,; and A;1, The rate constant of the fast process ot the experimental curve in Fig, 2 (a and b), d. is determined by all the three rate constants of the partial processes involved, i.c.. A^. A^. and Aq., (Giant/. 1979). An exact solution of this problem is complicated; it is included in the Appendix to, this paper as Eq. (39). However, under the assumption Al.- S> A./, A, (51 } i M linh ct al the system simplifies into: f) = Al;. <<*> Then A,; would amount to A,; = 20.7 h ' . (The solution derived in the Appendix results in A1; = 27.8 h"1.) To obtain Ai,, rearrangement of Eq. (19) ol T'ilser and Bolt (19X1) gives lienee, we obtain A;i = I.9X ir1. (Annin, the solution given in the Appendix results in a similar value; A;, = 1.77 h'r.) Translation of the Pharmacokinetic Data into "Open" Exposure Conditions After obtaining all the pharmacokinetic data for vinyl chloride in man under the conditions of the experimental system of Fig. la, a transition is necessary to the conditions of inhalation of the compound from an `'open" atmosphere, i.e.. F, --* -js (Fig. lb). Because the clearance term A,: F, (see Eqs. 2 and 3 of Filser and Bolt 1981) remains constant, this transition also implies A,;-- 0. Both AL., and As, remain unchanged. Also, it must be observed that A',, is dependent on the ratio IV^:- According to Ei|. (3h) of Filser and Bolt (19X1). A\, ot subject B cun be calculated for V/, -- 1 to be A.',, = 0.7 Id (I't -- *). For calculation of metabolic rates, we need knowledge of the actual concentrations in Cp; (Eq. 24 of Filser and Bolt, 1981), This is A\, v, when the final concentration in Cp? is reached on a continous atmospheric exposure to constant vinyl chloride levels. However, when regarding rapidly changing "peak concentrations" of exposure, the actual concentration in Cp: is determined by all the three processes of "influx", "efflux", and "metabolism" (Fig. lb). In order to simulate realistic "peak concentration" conditions, we calculated the actual concentration in Cpi as well as the cumulative dose of vinyl chloride metabolized for single clear-cut long-term and short-term exposures, as Fig, $*--d. Kinetic iinplicain constant exposure in low lev chloride (5 ppm for 2 h): () of atmospheric exposure, y,: (b) calculated concentration organism, yg (c) calculate dose metabolized. ,Vt<; (d) c cumulia've dose eliminaied t of unmetabolized vinyl chtori 13 Bo CO O \> fo b cn Kin. 4a--c. Kinetic implicaiioc tutmutiwnl r.xpautre lo "peak oncentrjuon\" of vim I chlori u*\.tmple of two peaks of 50 j mm each)- fa) conditions of .iinurtphcnc exposure, v,; (b) concentration in the organism. U") calculated cumulative doiC inctalxdi/cd. A* . -s.yw = 1.77 rV . 1 Conditions under the saryto the here, i.e.. 3 of Filser i. Both kei undent on subject B Kin. Ja-d. Kinetic implications o( i cnnsiant exposure to low levels nt vinyl chloride (5 ppm for 2h): (a) conditions of atmospheric exposure, y,; (b) calculated concentration in the organism. >y, (c) calculated cumulative dose metabolized. Arri; (d) calculated cumulative dose eliminated by exhalation of unmetabolized vinvl chloride he actual ! when the <posure to iing "peak ined bv all ib). calculated ,1 chloride ires, as Kii*. 4a--c. Kinetic implications of an oitertmueni exposure to '`peak soj^entrahons" of vmvl chloride t example of two peaks of 50 ppm for 'mm each): (a) condiMons of atmospheric exposure, y,; (l>) calculated concentration in the organism, yy Ic) calculated cumulative dose metabolized, St\ JO fio co roo ; ' fO o> Vfi ::u H, M Hull ct indicated in Fi^t. j and Hu. 4. I his c-ilcuJjiit>jj wus l>;isc*d an the lojfouinir cunsidcTitlion.s, I he- `'influx" (Fig. lb) which is determines! by Lcjv (2) and (.') of Fikcr and Boll (1981), remains constant as yt remains ai a constant value [i.e.. v, is fixed as see Eq. (.)): ./At ill -A'i A'..,, I '.r, = - ill < N) I be "efflux" (Fig. lb) is described bv Eq. (4) and (5) of Filser and Holt (19X1): r/A';;i ~k,, V ill The "metabolism" (Fig. lb), according to Eq, (24) of Piker and Holt (19X1), is: `IK, tit -A..,i K'"r.Vj (10) Hie change in the amount ot vinyl chloride being in Civ is the resultant of Eos (8-10): '" M </,V; (ly2 ~<it ~ : lit Kik;\ l':.V| - A;i I'm - " Aj.I'o-; . (ID I his dilterential equation is solved and divided by Ik: 2 -11' A'i A',,t\` i A': i + Aj -u * t ui (12) This equation describes the ascending section ol the concentration curve in Cp-> (from a to b in Fig. 4b). Alter ending the atmospheric "peak concentration", \q in Eq. (8) becomes zero, and the reached according to Eq. (12) at that time declines, due to the partial processes described in Eqs."(9) and (10). Hence, the course of Fig, 4b subsequent to point b is: It a second peak concentration occurs at a later time point (c) where residual vinyl chloride is stilt present in Cp;. some cumulation occurs as indicated in Fig. 4b. The amount ot vinyl chloride metabolized under such conditions is shown in Fig, 4c, It is given by the differential Eq, (10). For the section between time points a and b (Fig, 4c) this is solved into Viml Chloride * J `IK = A ,i(M -- I :A',.,y i a-J After time point bSi present in Cp^: {`IK - A., Ik/1 -5.* < / ' i, i The amount metabi -JjA is: A'oi/i -- j;. ! The Simulation of I 1 Following the above of vj. (c) the cumul-.j cumulative dose expi theoretically exposed | vinyl chloride (a), Thi * via metabolism and v 'j A,., and As, in this sul $ during and after this By contrast, in Fq ^ of 5 min each, and an that current technical .in alarm signal to bcf|ji trations at the works./ amount of vinyl chloriH (see Fig. 4c) was 40 uj (panel b) and of the The results of th*| ' ^ 120 -- WJO ppm x (Fig. ,'j: the intcrmiticrf in the same figure of suggest that. regardleJ formed from vinvl chlor ks. ii i curve in Cp: duration", Vj 2) at that time i). Hence, the (13) here residual indicated in ns is shown in oeiwecn time Following the above ways of calculation Fig. 3 demonstrates (b) the time course of y;, (c) the cumulative vinyl chloride dose metabolized (:VC|). and (ci) the cumulative dose expired, if subject B (Buchter el al. 1978; Buchicr 1979) were theoretically exposed for 2 h to the current TLV/TRK concentration of 5 ppm vinyl chloride (). The doses of vinyl chloride eliminated under these conditions via metabolism and via exhalation are very similar, because of the similarity ot ktt and k2\ in this subject. The overall amount of vinyl chloride metabolized during and after this (theoretical) exposure was 48 umol. By contrast, in Fig. 4 analogous compulations for two peaks concentrations of 5 min each, and amounting to 50 ppm, were made. It should be mentioned that current technical regulations in the Federal Republic of Germany provide an alarm signal to be given when actual atmospheric vinyl chloride concen trations at the worksite exceed the "TRK" for more than 5 min. The total amount of vinyl chloride metabolized during and after the two peaks of 50 ppm (see Fig. 4c) was 40 umol. Figure 4 demonstrates both the time course of y: (panel b) and of the cumulative amount metabolized (panel c). The results of the two calculations show that a constant exposure of 5 x 120 = 600 ppm x min led to 0.08 umol per atmospheric ppm per minute (Fig. 3); the intermittent exposure (Fig. 4) of 50 x 10 = 500 ppm x min resulted in the same figure of 0.08 nmol per atmospheric ppm per min. This would suggest that, regardless of the exposure profile, the amount of metabolites formed from vinvl chloride would solclv be a function of the mean vinvl chloride II \] It.'li ci concentration over time. If this were true, the amount ot vinyl chloride metabolized after ending an exposure should equal the difference ot metabolism between the theoretieal ease of steady-state and that amount actually metaholi/.ed up to arriving at the steady-state (or up to the end ot exposure) By use of an analog computer, this has already been shown for a series ot organic solvents by Droz and Fernandez (1977). The general validity of this rule is demonstrated by the following calculations. liquation (15) gives the metabolized amount during exposure, fit). (17) that after exposure. The sum of both. A't.|(lllU. represents the total amount metabolized during and after exposure. Hereby. y=(/,, in Eq. (17) is to be replaced by the expression of Eq. (12). Also, to obtain the entire amount metaholi/.ed, the t in Iiq. (17) must go towards 'Ihe result is: 'V'Uiiui _ " . . A; i + A.-i pL'.tki (IS) whereby i peak is the duration of the exposure peak and y, its (mean) concentration. The connection of and A.\, under conditions o| exposure to an open ttlmosphere is given by Eq. (3) of this paper and by Eq. (3b) of Filser ;tnd Bolt (lysi). Hence, it follows that t^otiitii -- A s,v ] 11A,. / peak (IV) According to the definition of A.',, (Eq. 7 in Filser and Bolt I9NI). this can be written ''on.in -- y.'l f peak (20) which, according to Eq. (24) of Filser and Bolt (1981). determines that amount which is metabolized during a time t after previous formation of steady-state conditions. Thus, it is clear that the mean exposure concentration over time is the only determinant for the amount of vinyl chloride metabolized, also under varying exposure profiles. Discussion The carcinogenicity ot vinyl chloride is the principle toxic effect which is relevant for the regulations covering the handling of this compound. This effect is due to reactive metabolites, most probably chloroethylene oxide, as mentioned in the Introduction section. A quantitative treatment of the comparative risk of different exposure profiles must consider that the actual amount or concen tration of chloroethylene oxide in the human organism is always a resultant of both formation by microsomal monoo.xygcnascsand breakdown by "detoxifying \ iml ( hlitfult* iV.ik { p;iihwa\V+- The concen the lime factor should F consequence, tor the 5* (Bolt et al. 1981a). The present data cl. exposures vs. peak cob. chloride metabolized r, epoxide formed is onb concentration over tirm provided they do not os 3J vinvl chloride metaboU fi lion). CO Because the conceit o ro n formation and by ret if present data that an -* r4o* .xposurc to vinyl chlon to processes and pathways Principally by using bio A possible way of tat et al. (1980). After Ri S-hydroxyethyl-N-accreb of the epoxide, in coif demonstrated a differ- exposure conditions. Ts direct action of glutafta characteristic species ca glutnthione-S-transfera< Bolt et al. 1981b) suggr- the capacity for a direct t with glutathione is limits possible immediate detox of vinyl chloride could f peaks which product* metabolite. Hence, necessary n encouraged bv our parts metabolite: a future ass- chloride exposure profit detoxication. Xppendix An enter '"0 1,1 a deter/ The partial process fr Filser and Boll (1981): sin I Ii et ill. doride solism ttuallv e). Bv rganic i owing ;, Eq. : nount to be 1> lount (18) lean) i e .] (! r i n be ? i j (20) ouni state \ only \ ying rani e to the ; of :cnt of kting i Viml i hhirulc I'eak ( niKvmr.nioiw pathways". The concentration of the reactive metabolite built up in the liver and the time factor should be critical lor the extent of alkylation at DNA sites and. in consequence, for the hepatic tumorigenic potential evoked by the xenobiotic (Bolt et al. 1981a). The present data dearly show that the exposure profile (e.g., commons low exposures vs. peak concentrations) docs not determine the net amount ot vinyl chloride metabolized and hence the amount of epoxide formed: the amount of epoxide formed is only a function of the integral of the atmospheric exposure concentration over time. This is valid also for very short concentration peaks, provided they do not exceed the range of 200 --300 ppm where saturation of the vinyl chloride metabolizing enzyme system must be anticipated (see Introduc tion). Because the concentration of vinyl chloride-derived epoxide is determined by formation and by removal (elimination) of this epoxide, it follows from the present data that an evaluation of differential risks of different profiles of exposure to vinyl chloride may reasonably be focussed only on the different processes and pathways by which the epoxide is eliminated. This must be done principally by using biochemical methodologies. A possible way of tackling this problem has recently been outlined by Muller et al. (1980). After suggesting that one urinary vinyl chloride metabolite. S-hydroxyethyl-N-acetylcysteinc, is formed directly by glutathione conjugation of the epoxide, in contrast to another metabolite, thiodiglyeolic acid, they demonstrated a differential excretion of both metabolites under differing exposure conditions. The validity of the underlying assumption of a possible direct action of glutathione on the epoxide could be proven by establishing characteristic species differences in hepatic microsomal (membrane-bound) glutathione-S-transferases (Bolt et al. 1981b). These data (Muller et al. 1981): Bolt et al. 1981b) suggest that in man, much in contrast to the situation in rats, the capacity for a direct detoxication of the epoxide formed from vinyl chloride with glutathione is limited only. This would indicate that, from the standpoint of possible immediate detoxication of the epoxide, low but constant exposure levels of vinyl chloride could possibly be less hazardous than marked concentration peaks which produce just the same integral amounts of the reactive metabolite. Hence, necessary further studies on this latter point are very much encouraged by our present evaluation of the kinetics of formation of the metabolite: a future assessment of the differential hazard of different vinyl chloride exposure profiles can be based almost entirely on the biochemistry of detoxication. Appendix An exact way to a determination of the rate constants Al;, k2]. and kcl. The partial process from Cpi into Cpj (see Fig. la) is given by Eq. (2) of Filser and Bolt (1981); similarly. Eq. (-1) of Filser and Bolt (1981) describes the II M Bull cl ,.l partial process Irom Cp; mio C'pf, Hence, the dunce of mass nt compound in Cp, with time. v ,,y' I ,, dyi 1 dt ~ ~ * | V| + (21) The change in Cp; is influenced by the three partial processes determined by AP. A':i. and Ad (Fig. la): tlv' K: d7i: = + Ai:K,y, - (Al: -r k,,)K:v. . (22) In this equation. lAv; may be replaced by dv, -- V, + k,:y,i; di Kits = - (23) which is derived from Eq. (21). Differentiation of Eq. (21) gives dr di dt (24) Equation (24). with Eqs. (22) and (23). leads to d~v i , , dvi "Tf + (kr_ + A;i + A\.|) + Ai;A\.lv, - 0 (It (it (25) This is a homogenous second order ditferential equation. The fundamental equation k~ + (A|; + A; | + A\.|)7. + A|;A.i = 0 has roots (26) (Ai: "r A;j + A..,) -- \/(A|. -r A';i + A..])" -- 4 A;;A.j (27a) and S irr. I ChloriU'- IY.it. Oh r; sT The general soluoot v, - r, c" + c %: This means that, at V||ii| = C'| + C; . - -y. *.?'. -. Ut ! ri 1; Differentiation of E` t,y; = k,C,S' + k dt 7 Because obviously t = 0: d.v..... -- -- Ai;yi,ui ilt From Eqs. (29) and From this equation. (27b): 30 I-- *i- - (* Kill c/) ii 10 From Eqs. (29) and j I cn _ .V|(nfi(tA|; + /'.| Again, t and /.2 are i ! A:i + ktj j; ' li'li - |, 1i i J I Hull Cl .it ipouml in I t <21; cdbyA'|i, (22) (25) (24) (25) i Jamental Vinyl Chloride Peak rnnccnlMlinm The genera) solution of Eq. (25) is V, = f| C'1 -r (\ This means that, at r = 0. 22? (2N) I'n.n = t'l + . (2V) Differentiation of Eq. (2S) gives r/v, = /.|( i<'*+ ?.( >i`*1. ill (5d) Because obviously i = 0: is zero, it follows Irom Eqs. (21) and (50) for `-h--------_---- Ai|.'V||,i, --_ /1( i + /-il i ill From Eqs. (20) and (51) we obtain (21) 5'iin) (^: + k\;) From this equation. /.| and /.> are eliminated bv inserting Eqs. (27a) and (27b): k)> - (fci + ktf) + V(A'i; + k;i + k^Y - 4 fct;A\i t I -- >'Idli -- -- - ,------------------ - ----------------- 2 v(k ly + A'y I + A`,)F -- 4 From Eqs, (29) and (31) we obtain for C:: (35) t I |-` W o ro u cNn) co 22(i Comparison ol Eqs. (36). {2b), ;ind (27b) reveals II M a J| - k' , I' I (see Eq. I), Jhoii. according to Eq. (27a), -7,( represents the rate constant of ihc tusi process in Eq. (I): - 7.i = <). (38) A combination of Eqs. (22). (25). (37). (38). and Eq. (28) give*, the evict formulation of .`V >'iini[A'i: " (A;i ! A\.|) f VfA't; + A_'| f A.i)' -- 2 A..A,.t| t`i = 3 V(A-,.'+ *77 + A\,r - 4 A,-A\, -,f- - -- -->'i(oi[A'^i + A\.| ---A-'i;--+--Vj..(A`i; +-k.;.i..i.-.A..,..if."..-. 4 A'l.'A,.,] (4 4j - V(Ai; + k:i + kti)* - 4 ki:ke\ (39) Figure 2a shows that the fast exponential process, determined by the rale constant d, is practically completed after 2(1 min (see above). At t = 20 min (Fig. 2a) y(,, was about 0.35 ppm vinyl chloride: the contribution of the first exponential partial function in Eq. (39) at that time point, is < 4.7 x to-1 ppm. Ihc further course of yq is, therefore, determined by the second exponential partial function in Eq. (29) only, and the extrapolation to vj,,,, (Fig. 2a) is justified. This means, for practical reasons. - .''[(it) (40) which was 0.668 ppm in the experiment of Fie. 2a. Hence, it follows (Eqs. 29 and 40): ( I ~ .Vtint (41) which was 9.332 ppm in the experiment. For determination of the rate constants of the partial processes (k!:. ktl. A-.,) the following calculations are made: Eqs. (29) and (31) are rearranged to give 3.,C, + A'i: - -- C, + C. (42i which is. with Eqs. (29). (37). (38). (40). and (41) A,,. -- - " t"iuii) >'lnM A'.vJ(h) (43) \m>l < hl*fhk` Peak Concert Hie numerical value tt A,.- - 27.S h"` . ; F.quation (26) is rearra , ~ 7.; -- A,(A|; 4 *ri = :----------- 7-r kf2 i' liquation (26) is rearra , -7.} - A:(A,: *"' ?!------------------- i . - fEquation (44) and (45) _ - A,A; h and. with Eqs. (37) aii| ***' - (k')'& " ki:(d-k') | I he numerical value t! A-t, = 2.03 h_1 (whic' % V.iih Eqs. (37) and (45j| , (A'): - A-'(A-,: 1 *md hence ihc numerical A:i = 1.77 h'1. U krumUd%fmtnt. The Julh 'w.iih-Hhmc We*ifjlia for fitul * **fl which the prevent c'l wifinMi" <f4ft( no. Bo 49| References \i (111. American Confercn t-duc* lur chemical whni| ( nhinAjii. Ohio, p 40 Mi tr .,1 l7) (he Iasi (JX) e exaci (.'W) ic rate in fl-ig. ic firsi 4 ppm. ncniial 2a) is (40) 2`) and (41) ti. ^:i) cod to (42) (43) Vinvl C hluritk' tVak ( orKcmr,i!umi. The numerical value thus obtained is ki; - 27.S h ' . Equation (26) is rearranged, and 7, (liq. 27a) is inserted instead .d 7: 7) - 7j(A|_' f A';i ) k.i -- `'"*12 (44) Equation (26) is rearranged under insertion of 7; (Eq. 27h) instead of 7: 7' - 7>(Ai; -f A\.|) -- k i *A..| k 7.* (45) liquation (44) and (45) give , _ 717j - 7;7: r' " A,;(7. -7,'j (46) and, with Eqs. (37) and (3X), _ d'k' - (k`)'d (47 J The numerical value thus obtained is kci 2.03 h-1 (which is the same as obtained above With F.qs. (37) and (45) we obtain ^ + Atl) + A|;Avl (4S) and hence the numerical value A;, = 1.77 h'1. AxkrumledgcmetU. The authors thunk the Ministry of Science and Research of ihc State l North'RhincAS'estfalia for financial support (pram no 11 BS-FA 6397; The biochemical research work on which the present evaluation \sas based was tunded by the "Deutsche Fors^hungsge* mcmschaft* (grant no. Bo 491/6*2). References AC tilH, American Conference of liovernmentai Industrial Hygienists (|9Mi) Threshold imut values for chemical substances in uorkrooin air adopted by ACGIH for 19mi. AC(iIII. Cincinnati, Ohio, p 40 R&S 024254 \mlervnii M\7. llnol D(i. K.ipl.in Nl. tI'INII) A yetier.il vtheme Inr the imnfpnr.uiMn nl ph.irin.ieiikineiiev in Inuilnvc rivk cvtiuuiunn Inr vlieum.il i.iiti'meeiieviv ev.uuple vmvl ehlnmlt- lmn.nl Appl 1'luirm.u.nl 55 154-ldl linker Gl., Keiler lip |P>77| Ainnituine vvvieuiv Inr mnriitnriue nml .hlnn.te n> unrkim: .iiniDvpherev All) Inti I Ivy Atvit' J .In 24-.U Hull JIM. lilver Ki, l..ul> III. < Jllemv.tltler II IIWI) llnuline kinciit;* i I vmvl lilnn.le .mu vmvl I'inimile .it verv Inw ilnvev Areh Invtenl |Suppt] 7 1 J'l I;7 Hull IIM. L.iih KJ. lilver Hi. Utienuuliler II. llueliler A il'MI.il Vmvl ihl.uiile .m,| tel.iteii enriipnuinlv ineeli.ttirvmv nl .retmii mi the liter 111 Cli.iliner> II . lleik I'll leilvt I riuuterv in liver iltve.ive. Ilneine Ntr-ittnii. New York (in prevvj Hull IIM. Ftlvor JG. Ocvth F. Guenthnei TM, Friuiil'v-ty I. Ilnli M tl'iNlhi Mei.itviliMerune vim \ inylchlnriil: Uniervelnetle /vvisehen Menveli untl Yerviiiliviicr un.l line tnviknlneivche Medeuluiijt. Verh Olvelt (iev Arheilsrnedr/m ((ienlner, Stuny.trl) Ini prew| llueliler A (I 7'/) Frirrhcriuity emer vpe/iellert rirhciivniedi/tnivehcti Llterw.iihirriyvuntervmhuni: in Korrcl.ilton /ur indiviiluellett VmvIeliltmd F.xptiMitnn I utvelumevheiivlu dev l..tmlev Niml. rheiii-Wevilnlen. F.nheruppe Mcdi/m, Nt.'SI.'. Wevuletiiveliet Vetl.iy. Opl.iden llueliler A. Unit IIM, Knppuv II. Ilnli W (1`I77) Die Gevvclivverteiluny \nn I J -1 '(`A'mvlehlnnd Ivr tier Kittle. lut Arch Oeeup Fnviruu lle.ilth .Id. 27-72 llueliler A. ilnli IIM. Ftlver Hi. Gneryeriv IIW. |,;nh KJ. Unit \V (|7m I'li.irimiknkmi tik uml Kiir/moyenese vnn Vmvlelilnrnl. Arheilsmedi/imvelie Kiviknheurteihmi; Verlt Dtv.h (iev Arlieilsmedi/nt ((ienlner. Sluiieait) IS. III-124 llueliler A. i-ilver JCi. Kcler II. Ilnli H.M (l'JX(l) I'hitriUiienkinehev nl vuivl ihlnride in fhe rlievuv nmnkey. Tuvienl Lett (r .7.7-71) l)l:Ci. Deulsdto Forsclninitviiemeiiiveluifl (I'JSII) In. Ileuveliler I) (llrvel M,.vm:.de Arlvitvpl.ii/. knn/enlralinnen. Il.iruld lloldi Verliiy, llnppard, p M Drnz PO, l-eriiande/ JG (I *177) Ulfeel nf phyxeal vvnrklnael mi reientmn .uul mei.iKdivm nl inhaled organic vulvenls. A enniparaiive thcureuenl .ippmueh ami dv applieaimnv with reeurJv it> exposure monitoring. Ini Arch Oceup linvirnn Health 7* ;i] - ;ai, lilver JG. Unit IIM (l`J71;) I'harniaenkmeliev of h.tloecn.ited elhvlenev m ratv Areh Itntienl 42:12.7-1.71) l ilver JG, Unit IIM (1 lJSIJ Inhalaiinn pliarmaenkineiiev haved nn eav uptake viudiev I Improvement of kinetic mnelelv. Arch Tovicol 47: 27') - 2'i2 Gehring l\l, Wat.iliahe KG, hark ( N (PI7S) Kevolutinn nf dovc-tevpmive tnvieitv ilata inr chemie.dv requiring metal'ulie activation: e\ample-vinvl ehlnrule 44 :.vS I-S'; | Invienl Appl I'h.irntaenl Gehring l*J. Wat inahe l`G. I'urk t'N (1'17`J) liivk nl angiov.n UMll.l m WUrleCTN CXpUM.`d lO chlorulc iis prciliotcU iroin niiuIics m r;iis. TomcoI Appl Phviriii.tkol -i't i.^-21 C il.im/ SA (I97*i) MiiiliciiKuu.'v lor hiomcUioal jppiic.UH>n> Univk'rMi> ul C.tiilorni.i I'rc^ licrklo * l.os Anodes l.oiulon (iuoniicrich FI*. C`r.^u>ril \VM, W.nanahc !*Ci (IW) Acio.ihon oi wn\l chloriUc u oiv.ik*n;l\ bound mciaboldo: uk`s ol ^vholurtclh\lciu.* oxide* and J-chlomacci.tMe'hxdo Hn>chcmisir\ IS: M77~_S1X2 llcnxchlcr O (|y7*)) Hcjircn^uni; xon Kon/cnif.mons'vpil/cn dcr CxpoMium ^ciicnuN'r eexund- hcits>cliadlichcn ArlH'iiNXlollcn (Kur/iciiwcnc) I. Vor^chlai: ^ur Uildum; Kalcconcn xon UbcTNchroitun^Nfaklorcn* */citcn und -h.iufi^kciicn Arbcu^mcd So/ialmcd Pravcntivnjcd M: ISI1-IV3 Muller (i. Ilciior Nt* Norpeuh K lieMimmuni: dor M>dn>\>Jthximcrkapiursiurc im Ham Vinvkhlorid-Exponierlcr. Mcthodiwhc lirlahrun^-n und anaKiiK'hc Erccbiuvse. Veih Dt^h Ccs ArK'iwmed (Gcn;ncr, Siuu^aru 'd /.ijdda F. Ook\ A. Harbin A. Malau'illo (.' I'omaiis L. H.irixh I! |i9,xii| CaranojjeniciH of chliUxurilnlciic oxide, an ultimate rcaiuvc tnetabolue oi \ui\I chloride, and hiMchloromc* thxllcther alter 'ubcuianeou,7 admiuiNtraiion and m tmtiaiHtn-proinouon exjn.nir.ent' in mice t'aiicer He^ 40'3S2-?5n Receded April 21. Il>Sl An Approach To* of the (Vtammaliar Angelika Ncuhuusor-Kl: Abtcilun^ fur Sau^cticrgeiKrti (icH'll'^haft lur Strahlcn- und |) Kiu2 NVuherberg. To^t Obt Zusammenfassung. C ak 2 Jahrzohntcn im suchc cntwickclt. Wa! [`cllflcckentcst cine v lichen somaiischcn M werden. Mil den in d wir die Absicht. die r des FeimeckentcstS f (T x HT)F, Embi b. cth. p. d und pc si I'cstsubstanz behande 33 Hmhryonalcntwicklun Gcnotypcn von Embr e co Emhryonen durchgel hcterozygvX sind. Die 0 IO im Alter von 3 \S'ocht I'rocarbazin verveendt IO 01 Cl Die niedrigsten in ken (vcrmuiliche somr .4 nalragcs induzierten. I'rtx-arhazin. Die Hiiul der lnaktivierung der gruppen des MC* unc glcich/cittg embryoto tier beohachteten MiB lung Die mil 5(1 mg/ vergleichbarc Empfi (C57BLAJUan x T)F, ^atk \upptnrJ h\ the Utn*